The present invention relates to the field of hydraulic transmissions. More particularly, this invention relates to a hydrostatic transmission which includes a pump and motor which are both disposed in one housing. Such a hydrostatic transmission provides considerable cost savings and reliability enhancements.
In U.S. Pat. No. 5,307,731, Chamberlain, et al., disclose a unitary housing system for hydraulic units. The housing is a single-cast, unitary, hollow housing which has a continuous sidewall extending between opposing forward and rearward walls to form an enclosed housing. The rotary axis extends longitudinally between the forward and rearward walls and is generally centered in an opening formed in the forward wall. Access openings are provided in the continuous sidewall transverse to the rotary axis for installation of the rotating group and other components during assembly. This housing system was developed to eliminate housing component joints along a path of major hydraulic separating forces. The housing system also eliminates fastening systems which would have been required along such joints.
The unitary housing concept was taken one step farther by Hansell in U.S. Pat. No. 5,540,563. Hansell discloses a unitary housing for a tandem pump. The unitary housing disclosed has a continuous sidewall connecting the end walls and at least tow apertures in the sidewall which allow insertion of rotating groups into the housing. Different mounting flanges can be provided at either end of the tandem pump. FIG. 5 of the U.S. Pat. No. 5,540,563 discloses that the two pump shafts are mechanically connected to each other by a coupling. Furthermore, no high pressure passages interconnect the two pumps through the center section. Each pump basically has its own separate, internal hydraulic system. The two pumps merely share a common input shaft or source of rotary power.
Despite these advances in eliminating troublesome joints and fasteners in hydraulic units, the above references fail to disclose how a unitary housing concept can be applied to a complete hydraulic or hydrostatic transmission which includes a pump and a motor fluidly connected together by high pressure passages. Conventionally, high pressure passages have typically been provided by external high pressure hoses which fluidly interconnect separately housed pumps and motors together. While it is known to combine pumps and motors together in a single package, such packages include more than one housing or include a housing which is split transversely to the axial forces generated by the unit. This arrangement causes reliability problems relating to the joints and fasteners, as discussed in the two patents mentioned above. Therefore, there is a need for a hydrostatic transmission, pump and motor, disposed in a single, unitary housing which lacks any troublesome transverse joints and associated fasteners.
Thus, a primary objective of the present invention is the provision of a hydrostatic transmission which includes a pump and motor disposed in a single, unitary housing.
A further objective of the present invention is the provision of a hydrostatic transmission disposed in one housing so as to provide a short package length.
A further objective of the present invention is the provision of a hydrostatic transmission in a single housing which has a porting web with high pressure passages extending therethrough.
A further objective of the present invention is the provision of a hydrostatic transmission that has a reduced number of fasteners and joints and thereby fewer opportunities for joint-related defects.
A further objective of the present invention is the provision of a hydrostatic transmission which has fewer components to machine and assemble.
A further objective of the present invention is the provision of a hydrostatic transmission which can be fabricated with fewer machining operations.
A further objective of the present invention is the provision of a hydrostatic transmission which has fewer fastener torquing operations during its assembly process.
A further objective of the present invention is the provision of a hydrostatic transmission which is easier to assemble, more economical to produce, and more reliable in use.
A further objective of the present invention is the provision of a hydrostatic transmission in which the pump and motor both have open cases such that oil is not generally retained in the housing.
A further objective of the present invention is the provision of a hydrostatic transmission having a unitary housing which incorporates side access holes for inserting the rotating groups into the housing.
A further objective of the present invention is the provision of a hydrostatic transmission in which all high pressure hydraulic connections are internal to the housing.
A further objective of the present invention is the provision of an improved trunnion bearing retainer.
A further objective of the present invention is the provision of a hydrostatic transmission in which the pump and motor shafts are not mechanically coupled.
These and other objectives will be apparent from the drawings, as well as from the description and claims which follow.